The present invention relates to a metal vapor source with a regulatable flow and to an ion analyzer equipped with such a source.
In an ion analyzer, a sample to be analysed is bombarded with primary particles (argon ions for example) to bring about the emission of secondary ions (positive or negative) which are quantitatively analyzed. It is known that it is possible to exult and stabilize the emission rate of secondary ions by saturating the sample surface with oxygen (in the case of positive ions) or alkali (in the case of negative ions). However, the controlled introduction of an alkaline vapor into an ion analyzer causes problems which have not hitherto been satisfactorily solved. The general procedure involves bombardment of the sample with alkaline ions (e.g. cesium ions) or prior deposition of alkali on the sample.
The first solution requires a change of the primary ion source on passing from positive ions to negative ions. Moreover, as has been found in the case of positive ions saturation is not obtained and the exultation rates may vary considerably depending on the operating conditions of the source and the penetration depth of the alkaline ions into the target.
The second solution only permits maximum exultation at a given time and does not permit the performance of continuous analyses and in particular the plotting of profiles.
The present invention obviates these disadvantages by proposing a metal vapor source and in particular an alkaline vapor source which makes it possible to obtain a regulatable vapor flow rate and which is well adapted to ion analyzers. However, it is obvious that the improved source according to the invention can be used in fields other than ion analysis and in particular in ion implantation.
Metal vapor sources which can be used in spectrometry installations are already known. U.S. Pat. No. 2,967,239 granted on Jan. 3rd 1961 and entitled "Method and apparatus for Analyzing Constituents of a substance" describes an ion source, constituted by a chamber connected to an analysis enclosure by a vapor supply pipe. Heating means permit on the one hand the regulation of the metal vapor pressure in the chamber and on the other prevent any danger of condensation on the inner walls of the pipe. Thus, the temperature of the latter is always higher than the chamber temperature.
French Pat. No. 1,341,917 (PV919, 342) granted on Sept. 23rd 1963 and entitled "Device for Introducing a Gas Sample into an Analysis Apparatus" describes a metal vapor source mounted on an analysis apparatus. This source comprises a chamber and a pipe for introducing vapour into the apparatus. This pipe can be heated by circulation of a flow along its wall in order to prevent condensation. In this case, the temperature of the pipe is above the temperature of the chamber containing the metal vapor.